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Research and ExplorationWorld's Fastest Monkeys

It's tough to get close to patas monkeys. Wily and skittish, they bolt at the sight of humans. The leggy monkeys, clocked at 34 miles an hour (55 kilometers an hour), easily eluded primatologist Lynne Isbell when she arrived in Kenya in 1992. "I thought I could keep up on a horse or a bicycle, but trees got in the way," she says. After six months of patient tracking on foot, Isbell was finally able to sit within yards of one patas group that lived on the Laikipia Plateau. And so began a ten-year missionthe longest continuous field study of little-known Erythrocebus patas.

As if on a high-speed biological clock, patas monkeys live fast, reproducing at the earliest age of any Old World monkey. Female patas reach sexual maturity at age two-and-a-half and give birth at three. Babies can survive alone at just six months, though they'll nurse for up to a year. Meanwhile, mothers mate and give birth again, every year. So a patas could be pregnant, nursing a baby, and shepherding a frisky juvenile all at the same time.

As mothers, patas range from doting to cavalier, says Isbell. They routinely hand off very young infants to other females, who babysit while the mother forages. But if an uninvited female comes too close to a baby, the mother will open her mouth, a silent threat meaning "keep away."

Only once in Isbell's ten-year study did the social order go drastically awry. Of eight babies born in 2000, three died from inept handling by females who stole them from their mothers. This followed a period of illness, low birthrates, and high infant mortality, when babies were scarceand perhaps coveted.

Though patas in captivity have lived past age 20, for adult females in Isbell's group the average age at death was four, with one-quarter dying each yeara surprisingly high rate. Early reproduction was critical for survival, she says. "They needed to replace themselves."

Patas thrive on the parched ranches of Laikipia, taking drinks from cattle troughs. The plateau's poor soils support woodlands of whistling thorn acacia trees, chief food source and shelter for the subspecies of patas (pyrrhonotus) that Isbell studied. The monkeys eat gum that oozes from the bark and ants that live in the trees' swollen thorns, as well as grasshoppers and other insects flushed from the savanna.

Unlike most primates, which sleep together in trees, patas and their young sleep alone and in a different acacia each night, a habit which may help them elude predators like leopards and domestic dogs.

In circuitous foraging, patas cover more ground (about four miles [six kilometers] a day) over larger home ranges (nearly 10,000 acres [4,050 hectares]) than any primate their size. Adult femalesaveraging 12 pounds (5 kilograms), about half the size of malesdirect the action of a group, commonly 20 females and their offspring, and one rather peripheral adult male. Isbell's group fell from 51 monkeys at its peak to seven and now mingles with a neighboring group.

Laikipia supports 300 to 500 pataslikely the largest, most stable population in Kenya. But as Kenya's human population grows, acacias may be toppled for farmland and charcoal. Given their vulnerability to natural fluctuations, patas can't afford any new man-made threats.

Lisa Moore LaRoe

Web Links

Laikipia Wildlife Forumwww.laikipia.org/Learn more about the Laikipia Plateau and this conservation group that unites area ranchers, pastoralists, representatives from small farming communities, the Kenya Wildlife Service, NGOs, and the government. The site includes a map of the Laikipia Plateau.

Abstract of Lynne Isbell Paperwww.laikipia.org/patas-monkeys_june2003.htmRead the abstract of "Distribution and Abundance of Patas Monkeys in Laikipia, Kenya," a paper Lynne presented to the Laikipia Wildlife Forum in May 2002.

Bibliography

Isbell, Lynne. "Diet for a Small Primate: Insectivory and Gummivory in the (Large) Patas Monkey (Erythrocebus patas pyrrhonotus)," American Journal of Primatology (1998), 381-98.